1. Field of the Invention
The present invention relates to a process for manufacturing molded objects with better short time deflection temperature under load properties, as well as the molded objects manufactured by the process of the invention.
2. Description of the Background
In the electric and electronics industries, the demands placed on high dimensional stability of certain molded objects with high short term heat loads has increased because of the employment of various soldering processes in the manufacturing process such as reflow or wave soldering. Here, temperature peaks of 260xc2x0 C. to 450xc2x0 C. occur within a time window of up to 30 seconds. This especially applies to SMD components (surface mounted devices) and MIDs (molded interconnect devices, i.e. spatial circuit carriers). The glass fiber reinforced and self-extinguishing molding compounds based on polyesters such as polybutylene terephthalate that are generally used in the electric and electronic industries for this application only satisfy these requirements to a very limited degree. This is especially the case when lead-free solders are used, where the soldering temperature employed is approximately 30xc2x0 C. higher than the temperature employed during soldering when solders are used that contain lead.
A higher degree of stability can be achieved for molded objects that are subject to heat loads by irradiating them with xcex2 or xcex3 rays. The reason for the higher degree of loadability is probably attributable to the crosslinkage of the polymer skeleton. To increase this effect, crosslinking agents are generally added as an additive. Crosslinkage is also achieved by irradiation when the polyester molding compound contains olefinic covalent bonds in the polymer skeleton. These crosslinking sites can be introduced through copolycondensation with unsaturated monomers such as 2-butane-1,4 diol when the polyester is being manufactured. Molded objects such as this are described in EP-A 0 559 072, EP-A 0 669 360, and EP-A 0 679 689. The disadvantages of the irradiation process are obvious: it requires expensive equipment and generally requires an additional logistics process, because the objects are usually irradiated by a manufacturer different from the manufacturer of the molded objects, thus making the process expensive and time consuming. Accordingly, a need continues to exist for a method of manufacturing such molded objects which is simpler and of lower cost.
Accordingly, one object of the present invention is to provide a method of manufacturing molded objects which avoids the difficulties mentioned above and, in particular, enables even higher heat loading during the process of manufacture.
Another object of the present invention is to provide molded objects of high dimensional stability.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a process for manufacturing a molded object, comprising:
a) preparing a shaped object by molding a formulation of:
35 to 100% by weight of a thermoplastic polyester,
0 to 60% by weight of filler or a reinforcing material,
0 to 20% by weight of an impact modifying rubber,
0 to 30% by weight of a flame retardant,
0 to 20% by weight of a synergist and
0 to 5% by weight of other additives and/or processing agents; and
b) treating the molded object for at least 1 hour at a temperature ranging from 180 to 250xc2x0 C., thereby preparing a molded object with improved short-time deflection temperature under load properties.